Method of forming printing stencil



Jan. 2,1968v M.MICHALCHIK I 3,361,058

METHOD OF FORMING PRINTING STENCIL Filed Oct. 17, 1966 m F'G'Z NEGATIVE 9 HIGH r I VOLTAGE 2 SOURCE 0 004000000 OOOOOOOOOOOOOOO l D souac;

I5 ooooooo "6aai5% ooooo "835 66 006x10 HEAT SOURCE j United States Patent 3,361,058 METHOD OF FORMING PRINTING STENCIL Michael Michalchik, Bethpage, N.Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Filed Oct. 17, 1966, Ser. No. 587,116 7 Claims. (Cl. 101128.4)

fore been proposed for forming such stencils or screens in V which a fine mesh screen is coated with a photoresist material and then exposed to form an image thereon. The latent image is then developed and the screen washed to remove the unexposed portions of the photoresist. The

pattern of areas of the screen from which the photoresist has been removed then serves as a screen through which ink or other printing medium may be brushed. However, stencils formed by such a process are of limited durability and are not usable at relatively high temperatures.

It is an object of the invention, therefore, to provide a new and improved'method of forming a printing stencil which obviates the above-mentioned disadvantages of stencils formed by prior methods.

It is another object of the invention to provide a new and improved method of forming a printing stencil which yields a stencil of long life and one usable at relatively high temperatures.

In accordance with the invention, there is provided a method of forming a printing stencil which Comprises forming an image-representative pattern of insulation material on a conductive plate, charging the surface of the insulation material nonadjacent the plate to a relatively high electrical potential, disposing a reticulate conductive screen closely adjacent and parallel to the charged surface of the insulation material, applying to the conductive screen a relatively low electrical potential of the same polarity as the charge on the surface of the insulation material, applying to the conductive screen a comminuted fusible nonconductive material of a size capable of passing through the screen, such comminuted material tending to collect in the screen over areas corresponding to the charged surface of the insulation material, and fusing the collected comminuted material to the screen.

For a better understanding of the present invention, together with other and further objects thereeof, reference is had to the following description, taken in connection with the accompanying drawing, while its scope will be pointed out in the appended claims.

Referring to the drawing:

FIGS. 1 to 5, inclusive, comprise a schematic representative of the several steps utilized in practicing the method of the invention.

Referring now more specifically to the drawing which represents a method of forming a printing stencil in accordance with one embodiment of the invention, the first step represented in FIGS. 1 and 2 comprises the forming of an image-representative pattern of insulation material on a conductive plate 10. In FIG. 1, the plate 10 is shown as coated with a layer 11 of any well-known photoresist material which has insulating properties. The layer 11 is shown as having portions 11a which have been exposed by an image to be printed. After the layer 11 has been developed and washed, the exposed portions 11a of the insulation area remain adherent to the plate 10 as shown in FIG. 2.

As represented in FIG. 3, the surface of the portions of the insulation material 11a nonadjacent the plate '10 are charged to a relatively high negative electrical potential. For example, a conductive mesh or screen 12 may be disposed directly over the plate 10 and closely adjacent thereto and connected to a negative high-voltage source 13. Either by electrostatic induction or by corona discharge, the upper surfaces of the portions 11a of the insulation material develop a high-voltage negative charge represented schematically by the dash lines 14.

The next step in the process embodying the invention is represented schematically in FIG. 4 in which a reticulate conductive screen -15, for'example a wire mesh, is disposed adjacent and parallel to the charged surfaces of the portions 11a of insulation material. As shown in FIG. 4, the screen and the plate are preferably disposed horizontally. A relatively low negative potential is then applied to the screen 15 from a voltage source 16.

As shown in FIG. 4, there is then applied to the screen 15 a comminuted fusible nonconductive material 19, such as resin-coated glass beads, of a size capable of passing through the screen 15. To this end, there is provided a reservoir 17 for the comminuted nonconductive material and a cooperating spreading drum '18. The unit 17, 18 and the plate 10 are relatively movable horizontally back and forth so that the nonconductive material 19 is distributed uniformly over the screen 15 by gravity.

It has been discovered that if the charges 14 built up on the upper surfaces of the portions 11a of insulation material are substantially higher than, but of the same i polarity as, the potential of the source 16, the comminuted material 19 tends to collect as deposits 20 in the meshes of the screen -15 directly over areas corresponding to the charged surfaces of the portions 11a, 11a of the insulation material while, over the remaining portions of the surface of the plate 10, the comminuted material 19 falls through, resting on the plate 10 as represented by the deposits 10a, 10a.

The deposits 20 of the collected comminuted material are then fused to the screen 15 by the application of heat, as represented schematically in FIG. 5.. It is important that the screen 15 be of material compatible with the comminuted material to be fused thereto. For example, if the comminuted material is a resin, the screen 15 may be a bronze wire mesh. If the comminuted material is of glass, for example glass heads, the screen 15 may be of a wire mesh of a metal having a temperature coeflicient of expansion comparable to that of glass, for example platinum or an iron-nickel-cobalt alloy such as described in Patent 1,942,260 and available under the name of Kovar from Westinghouse Electric Corporation and Fernico from General Electric Company. In a preferred method of forming the printing stencil, the glass beads are coated with a resin, in which case it is also preferable to conduct the fusing operation at a high temperature wtih the screen supported on a flat refractory surface and in the presence of the saturated vapor of a solvent for the resin, for example trichlorethylene.

While the method of the invention may be practiced by employing the several steps the parameters of each of which may be varied over a range of values, there follow the specifications of one group of parameters which have yielded a satisfactory printing stencil in accordance with the invention:

Induced charges 14 800 volts. High-voltage source 16 -400 to -600 volts. Screen 15 325 to 400 mesh bronze Wire mesh.

3 Spacing between screen 15 and plate 10 to 15 mils. Comminuted nonconductive material 19 Soft glass beads 5 to 30 microns in diameter coated with an hydroxy functional silicone resin such as resin Z6018 commercially available from the Dow Chemical Company containing 0.1% of iron naphenate by Weight of resin, the resin constituting 5 to 30% by Weight of glass. Fusion of nonconductive material 19 to screen 15 3 minutes at 260 C. in the presence of saturated vapor of trichlorethylene.

While there has been described what is, at present, considered to be the preferred embodiment of the invention, it Will be obvious to those skilled in the art that various changes and modifications may be made therein, without departing from the invention, and it is, there fore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The method of forming a printing stencil which comprises:

forming an image-representative pattern of insulation material on a conductive plate;

charging the surface of said material nonadjacent said plate to a relatively high electrical potential; disposing a reticulate conductive screen closely adjacent and parallel to said charged surface;

applying to said screen a relatively low electrical potential of the same polarity as the charge on said surface;

applying to said screen a comminuted fusible noncond'uctive material of a size capable of passing through said screen, said comminuted material tending to collect in said screen substantially only over areas corresponding to said charged surface;

and fusing the collected comminuted material to said screen.

2. The method of forming a printing stencil in accordance with claim 1 in which the reticulate screen is a wire mesh.

3. The method of forming a printing stencil in accordance with claim 1 in which the potentials of said surface and of said screen are negative potentials.

4. The method of forming a printing stencil in accordance with claim -1 in which the comminuted material consists of resin-coated glass beads and the screen is of metal.

5. The method of forming a printing stencil in accordance With claim 1 in which said screen and said plate are disposed horizontally and said comminuted material is distributed over said screen by gravity.

6. The method of forming a printing stencil in accordance with claim 1 in which the comminuted material is fused to said screen by the application of heat.

7. The method of forming a printing stencil in accordance with claim 1 in which the comminuted material consists of resin-coated glass beads fused to said screen in the presence of the vapor of a solvent for the resin.

References Cited UNITED STATES PATENTS 2,860,576 11/1958 Short 101128.3 2,949,848 8/1960 Mott 101128.3 2,949,849 8/1960 Gundlach 101128.3

FOREIGN PATENTS 704,148 2/1954 Great Britain.

DAVID KLEIN, Primary Examiner. 

1. THE METHOD OF FORMING A PRINTING STENCIL WHICH COMPRISING: FORMING AN IMAGE-REPRESENTATIVE PATTERN OF INSULATION MATERIAL ON A CONDUCTIVE PLATE; CHARGING THE SURFACE OF SAID MATERIAL NONADJACENT SAID PLATE TO A RELATIVELY HIGH ELECTRICAL POTENTIAL;ADJADISPOSING A RETICULATE CONDUCTIVE SCREEN CLOSELY ADJACENT AND PARALLEL TO SAID CHARGED SURFACE; APPLYING TO SAID SCREEN A RELATIVELY LOW ELECTRICAL POTENTIAL OF THE SAME POLARITY AS THE CHARGE ON SAID SURFACE; APPLYING TO SAID SCREEN A COMMINUTED FUSIBLE NONCONDUCTIVE MATERIAL OF A SIZE CAPABLE OF PASSING THROUGH SAID SCREEN, SAID COMMINUTED MATERIAL TENDING TO COLLECT IN SAID SCREEN SUBSTANTIALLY ONLY OVER AREAS CORRESPONDING TO SAID CHARGED SURFACE; AND FUSING THE COLLECTED COMMINUTED MATERIAL TO SAID SCREEN. 